[VinnyP]

The quality is relative whilst in tests the Nikor 12-24 is marginally better optically than the 10-20 Sigma the Sigma still is a quality piece of glass and the extra 2mm makes a huge difference. Maximum aperture means much less in a wide angle unless you are photographing movement. But as I said it's relative, the Sigma 10-20 is a much better lens than either of the kit zooms you are currently using and the 105 is miles ahead, optically little else touches it. It falls down on internal focusing and the amount it extends. The new Nikkor 105 VR is awesome but there is almost no advantage optically over the Sigma. As for handling and VR it's a dream, but at a price.